It's perfectly possible to edit Admin4 sources with your favorite text editor, but using PyDev is recommended. Please note PyDev's prerequisite, it requires Eclipse to run under Java7.
After all runtime requirements are installed, you can pull the sources from GitHub and start debugging.
The Eclipse/PyDev settings are as follows:
Eclipse's Git integration will give you access to the sources from GitHub, using git://github.com/andreas-p/admin4.git. You'll need the platform specific python modules, as described in the previous chapter, as well.